Composite structures comprising superabsorbent material are well known, in particular for applications in absorbent articles, such as disposable absorbent articles, such as baby or adult incontinence diapers, feminine hygiene products, food pads, bed pads, pet pads and the like. In addition to effectively and efficiently satisfy the primary liquid handling functionality of acquisition, distribution and storage of the exudates, the perception and acceptance by the user, in particular for a wearer, such as with regard to wearing comfort or discreteness has become more and more an area of attention.
In particular for absorbent disposable articles, there has been recently a trend towards thinner articles. In this context, superabsorbent materials (SAM) have been used in increasing concentrations, initially without majorly changing the design principles of the articles or of the production facilities.
In this context, first limitations by superabsorbent properties have been addressed such as described in WO95/26209 (P&G, Goldman) and products with a maximum concentration of up to about 60 weight-% of SAM particles became broadly distributed, if not a standard in baby diapers. Such structures allowed production on existing diaper manufacturing equipment, where the SAM and the cellulosic fibers were mixed in-line, i.e. the SAM particles were provided in bulk form to the manufacturing plant and mixed with defiberized cellulose. Then an absorbent core was formed and directly combined with chassis elements like topsheet and backsheet for making a finished diaper.
Taking the minimization of cellulosic fibers to the extreme resulted in the “air felt free” technology, where at least the liquid storage component of an absorbent article is essentially free of cellulosic fibers. This has been described e.g. in EP725613A1, EP725615A1, EP725616A1, EP724418A1 (all K-C, Tanzer); EP1621165A1, EP1621166A1 (P&G, Blessing); WO2012/048878A1 (Romanova BvBA Starter, van de Maele), all disclosing pocketed structures with superabsorbent particles sandwiched between webs. In order to satisfy manufacturing and in-use requirements the SAM particles are immobilized by positioning these in “pocket structures”, optionally by the application of adhesive.
However, such structures have some drawbacks. So they require particular and sometimes complicated process measures to satisfy modem high speed production requirements. Further, they require particular measures with regard to fluid handling as such high concentration superabsorbent structures are limited in their ability to distribute liquid. Also measures need to be taken to immobilize the superabsorbent particles both in their dry and in their wet state. Even further, such structures may exhibit a hard feel to the user, as the particulate material may give a hand, which may be referred to as “sanding paper” like.
Yet a further approach of improving absorbency has been followed in the field of air-laid materials. Such materials are also well known in the art and are broadly commercially distributed. They also comprise cellulosic fibers, and often SAM. However, such materials are typically produced “off-line” and shipped as a composite to a converter, who may form absorbent articles, but also other absorbent products such as food tray pads.
Airlaid materials may—and often do—comprise binder materials so as to enhance the mechanical stability and SAM immobilization at least in the dry state, often also in the wet state. Typically airlaid materials exhibit very good softness and feel to the touch.
In EP1032342A1 (Maksimow) structures are described, which may comprise up to 70% of particulate SAM, the remainder being cellulosic fibers. The binding of the structure is described to be essentially only achieved by “fusion bonding” between cellulosic fibers, induced by the residual moisture of the fibers and a high compaction pressure.
In WO99/49826 a C-folded layered absorbent core is described, wherein an absorbent layer is positioned between an upper and a lower layer. These latter layers may comprise latex as a bonding agent. Whilst the absorbent layer may exhibit SAM concentrations of up to 95% by weight, the total absorbent core exhibits SAM concentrations of below 70% by weight.
In EP1721036A1 (Glatfelter, Hansen) the manufacturing of fibrous webs with low dustiness and good liquid handling and mechanical strength is described. To this end, a mixture of SAM particles and cellulosic fibers can be sprayed on both sides with a high moisture content latex dispersion. Upon embossing and drying, optionally combined with vacuum suction for a controlled penetration of the latex dispersion or at least the water phase thereof, three bonding mechanism are described to take place: First, the “self bonding” of pressure bonding due to the natural moisture of the fibers. Second, the outer regions of the web as exposed to the latex resin are bonded upon curing of the latex. Thirdly, the penetration of the moisture into the web further creates hydrogen bonding.
As the bonding mechanism relies on fiber-to-fiber bonds, this approach is—similar to the technology as described in EP'342 (Maksimov)—limited to a maximum SAM particle concentration of about 70%
In spite of all these approaches, there is still a need for providing an absorbent structure which provides high absorbency by exhibiting high concentrations of SAM in excess of 70%, which exhibits good liquid handling properties but also good tactile properties.
There is also a need for providing such materials for being included in disposable absorbent products.
Even further, there is a need for an easy and effective manufacturing process for such structures, which may be also be executed for the manufacturing of off-line air-laid structures.